This invention relates generally to gas turbine engines and, more particularly, to determining operating parameters for controlling gas turbine engines.
In at least some known rotatable machines for example, a gas turbine engine, turbine blade and/or nozzle temperatures have to be limited to ensure safe operation of the gas turbine engine and to ensure desired life for engine components. However, because of the adverse environments where these components operate, the temperatures are not measurable using thermocouples or RTDs, the traditional techniques for measuring gas path temperatures.
One known technique used on current production engines involves measuring exhaust gas temperature (EGT) downstream of the high-pressure turbine components at a location cool enough for a temperature probe to survive. This technique is prone to sampling problems, thermal lags in the probes, and errors in correlating the measured gas temperature to the desired metal temperature upstream. Moreover, as gas-path temperatures increase, probe life is reduced and cost increases. A second measurement technique uses a pyrometer to measure the metal temperature of interest. This technique is expensive and is subject to problems with line of sight, lens fogging, and sensing system unreliability.
Aircraft engines are designed to provide specified levels of thrust, but thrust cannot be measured. Hence, thrust is inferred from a measurable thrust-setting parameter such as fan speed or engine pressure ratio. In certain applications, such as in aircraft capable of short takeoff and vertical landing, it is highly desirable to control thrust directly, rather than through the control of speed or pressure ratio. This requires that the engine's control system have a means for estimating thrust accurately.